Jeff Hiller
COMSOL Employee
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Posted:
3 years ago
01.04.2022, 13:45 GMT-4
Hello 宇宣,
What the Rigid Motion Suppression node does behind the scenes is that it imposes point constraints that just eliminate the 6 rigid body motions that a 3D structure would otherwise have (See this blog post for more information). The eigenmodes of the thus-constrained structure will respect those constraints and therefore depend on those constraints.
You can think about it this way also:
There's more than one way you can pick point constraints to eliminate the 6 rigid body motions. While the Rigid Motion Suppression feature in COMSOL picks a particular set of point constraints, you could certainly manually pick a different set of points to impose constraints on to eliminate those 6 rigid body motions (or use the same points but impose different constraints). Each such set of constraints will result in a different set of eigenmodes.
To obtain the eigenmodes of your structure, you should apply constraints that correspond to the real-life situation, not use Rigid Motion Suppression.
Best,
Jeff
-------------------
Jeff Hiller
Hello 宇宣,
What the Rigid Motion Suppression node does behind the scenes is that it imposes point constraints that just eliminate the 6 rigid body motions that a 3D structure would otherwise have (See [this blog post]( https://www.comsol.com/blogs/modeling-parts-without-constraints-in-your-structural-analyses) for more information). The eigenmodes of the thus-constrained structure will respect those constraints and therefore depend on those constraints.
You can think about it this way also:
There's more than one way you can pick point constraints to eliminate the 6 rigid body motions. While the Rigid Motion Suppression feature in COMSOL picks a particular set of point constraints, you could certainly manually pick a different set of points to impose constraints on to eliminate those 6 rigid body motions (or use the same points but impose different constraints). Each such set of constraints will result in a different set of eigenmodes.
To obtain the eigenmodes of your structure, you should apply constraints that correspond to the real-life situation, not use Rigid Motion Suppression.
Best,
Jeff
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Posted:
3 years ago
02.04.2022, 01:02 GMT-4
Updated:
3 years ago
02.04.2022, 01:08 GMT-4
Hi Jeff,
Thank you so much, you solved my big problem!
But I have one more question here.
I have a piezo disc and I want to get its eigenfrequencies, since the disc is operating in the water tank, should I model the disc with water domain, and run the eigenfrequency study for piezoelectricity and acoustic-structural coupling multiphysics or just model the disc? And if the water domain is necessary, should I add the PML since the water tank compare to the disk is infinite domain?
Thank you again!
Hello 宇宣,
What the Rigid Motion Suppression node does behind the scenes is that it imposes point constraints that just eliminate the 6 rigid body motions that a 3D structure would otherwise have (See this blog post for more information). The eigenmodes of the thus-constrained structure will respect those constraints and therefore depend on those constraints.
You can think about it this way also:
There's more than one way you can pick point constraints to eliminate the 6 rigid body motions. While the Rigid Motion Suppression feature in COMSOL picks a particular set of point constraints, you could certainly manually pick a different set of points to impose constraints on to eliminate those 6 rigid body motions (or use the same points but impose different constraints). Each such set of constraints will result in a different set of eigenmodes.
To obtain the eigenmodes of your structure, you should apply constraints that correspond to the real-life situation, not use Rigid Motion Suppression.
Best,
Jeff
Jeff Hiller
Hi Jeff,
Thank you so much, you solved my big problem!
But I have one more question here.
I have a piezo disc and I want to get its eigenfrequencies, since the disc is operating in the water tank, should I model the disc with water domain, and run the eigenfrequency study for piezoelectricity and acoustic-structural coupling multiphysics or just model the disc? And if the water domain is necessary, should I add the PML since the water tank compare to the disk is infinite domain?
Thank you again!
> Hello 宇宣,
>
> What the Rigid Motion Suppression node does behind the scenes is that it imposes point constraints that just eliminate the 6 rigid body motions that a 3D structure would otherwise have (See this blog post for more information). The eigenmodes of the thus-constrained structure will respect those constraints and therefore depend on those constraints.
>
> You can think about it this way also:
>
> There's more than one way you can pick point constraints to eliminate the 6 rigid body motions. While the Rigid Motion Suppression feature in COMSOL picks a particular set of point constraints, you could certainly manually pick a different set of points to impose constraints on to eliminate those 6 rigid body motions (or use the same points but impose different constraints). Each such set of constraints will result in a different set of eigenmodes.
>
> To obtain the eigenmodes of your structure, you should apply constraints that correspond to the real-life situation, not use Rigid Motion Suppression.
>
> Best,
>
> Jeff
>
> -------------------
> Jeff Hiller